Kelly Reichardt makes small, hushed films about the invisible flotsam of the American west. Her natural subjects are the drifters and the outcasts, the barely getting by. Her natural habitat is the lonesome campfire and the railroad track. She says she lives like a bum, she makes hardly any money. Her very presence at the Venice film festival, I’m guessing, is the result of some ghastly administrative error.

But here is the paradox. With each passing film, Reichardt finds herself hauled out of the shadows and nudged towards the mainstream. The murmurous, mesmerising Old Joy made way for the wrenching Wendy and Lucy, which stranded pensive Michelle Williams on the fringes of town. This in turn was overtaken by the acclaimed Meek’s Cutoff, a western with a difference, marooned in the desert. Reichardt’s pictures creep up on audiences, but they are so potent and so haunting that they prove hard to ignore. They call out to the world, perhaps louder than she’d like.

The latest, Night Moves, is the most clamorous of all, in that it boasts a pair of rising young stars and a plot that might briefly be confused for that of a high-concept thriller. Jesse Eisenberg and Dakota Fanning are a pair of corn-fed eco-activists who hatch a plot to blow up a hydroelectric dam in the forest. Meanwhile the film darts, head down, from the organic farm to the feed store to the woodland lake where the time-bomb is ticking, across an Oregon interior the director has been mapping for years. We are never quite sure whether the plan will come off. We are never even certain whether these crusaders are intended to be read as heroes or villains. Night Moves plays its cards close to its chest and implicitly asks the audience to deliver a verdict.

It is the last interview of the day, although Reichardt has yet to settle. She curls her slender frame into a corner of the couch and tugs her knees to her chin, apparently determined to take up as little space as possible. Night Moves, she explains, is the perfect Oregon story because the Pacific Northwest feels like the environmental frontline. It’s last gasp of the old frontier, a clashing contrast of civilisation and nature, industry and activism. “It’s all right in your face,” she says.”There’s always a train going by with a forest of redwoods on the back of it. Or you go into the cities and you can smell the lumber plants everywhere.” I suspect she would quite like to be there, hanging out in the hippy farm or the lumber yard. Anywhere other than this Venice hotel with its polished fittings and the gondolas gliding by on the canal at our backs.

She was raised on the east coast, in Dade County, Florida. Her parents were cops (Dad a crime-scene investigator, Mum a narcotics agent) but they broke up when she was young; both started new families, and she basically feels she has been rattling loose ever since. She’s based in New York, but she shoots out west. When she’s not leading a film crew across the desert, or through the woods, she supplements her income by teaching at a number of liberal arts colleges.

The students, she suggests, regard her as a bit of a crackpot. They are so grounded, so groomed, so perfectly content. They would never dream of riding the box-cars to Alaska, let alone attempt to bomb a dam to make a political point like the activists in Night Moves. “I don’t see much concern or interest,” she says. “I mean, granted, I’m around kids who can afford to go to these fancy colleges. But the kids I know, I love them, but they’re not mad the way we used to be. They like their parents. They have plenty of money. They seem so unafraid and so un-angry. It makes them very nice people. It doesn’t make for great art. I ask them all the time: ‘Aren’t you mad at anything?’ They look at me like I’m off my rocker.”

My sense is that she rather relishes the role of outsider. The very notion of success appears to cause her discomfort. “Well, that depends what we think of as success,” she counters. “I mean, I think the films are both imperfect and successful in showing the parts of life that we don’t often see on screen. To me, it’s a case of: is the scene successful? Is the shot successful?”

OK, but that’s not what I meant. The very fact that Reichardt gets these movies made – the simple fact that she is here in competition at the Venice film festival – makes her a highly successful director, whether she likes it or not.

“All right, good,” she shrugs. “I’ll take it. But what’s success? Every time I make one of these films I assume it’s the last. Especially after Meek’s Cutoff, I thought I’ll never make another one. Here I am dragging these actors through the desert and we can’t even see their faces; clearly this isn’t working. But yes, it has allowed me a nice teaching job. I don’t own anything, if that’s your measure of success. But I have a good life. I have an interesting job. I get to make these films with people I love.” She thinks it over. “Look, if you’re from Florida and you get out of Florida and build a life full of interesting people, then you’re successful already. The rest is just a bonus.”

I’m betting Night Moves will not be the last film she makes. But who can say? The future is uncertain and the way ahead is dark. And one of the things I love about Reichardt’s pictures is their devastating deployment of the hanging ending. I’m thinking of wonky Kurt (beautifully played by the singer Will Oldham), left wandering city streets at the end of Old Joy, hapless Wendy, still looking for Alaska, or Meek’s Cutoff’s lost pioneers, forever strung between triumph and disaster. These films do not so much resolve as dissolve. They leave us dangling, forced to write their third acts in our heads.

Reichardt does not know why her movies have a tendency to turn full circle. She blames her regular collaborator, the writer Jon Raymond, but she’s only joking; it is her own fault as well. “Maybe I’m suspicious of absolutes,” she concedes. “I mean, yes, there is something satisfying about watching an old film when the music rises up and the words come at you – The End. But it would seem absurd to do that at the end of one of my films. It would just make them feel lopsided, because they’re all so short, they cover so little time. We don’t know where these people were before. We spent a week with them and then on they went. My films are just glimpses of people passing through.”

She admits that she sometimes finds herself thinking of these characters and wondering what on earth they’re up to now. Some of them, she suspects, reflect her own personality. “I remember when I was first trying to make Night Moves, I was working at it for a year and it just wasn’t happening,” she recalls. “I’m 49 years old and I’ve gone out to Oregon and in the course of eight months I stayed in 21 different places. And I thought: Jesus, I’m nearly 50 and here I am still couch-hopping. I’m so pathetic; this is such a pitiful existence. I’ve finally outdone the Kurt character in Old Joy.”

She doesn’t know what she is going to do. The meter is running; she can’t couch-hop all her life. She ought to knuckle down and make some proper money. At least Night Moves, I suggest, might provide her ticket to the big time. It’s got Jesse Eisenberg, Dakota Fanning and a ticking time-bomb at its centre. If Night Moves can’t secure her a directing gig on the next Spider-Man picture, then I don’t know what will.

Reichardt looks aghast. She wonders whether I’m serious. A director-for-hire on a studio blockbuster? As if that would be the best possible solution for her so-called career. As if it would even happen anyway; the very prospect makes her snort. “Put it this way,” she says. “There is as much chance of them calling you up to ask you to direct Spider-Man as there is to call me. I’m not even kidding, they’d call your number first.”

I don’t believe this for an instant, and yet Reichardt just might, or at least she might need to. She has to feel that she is still out on the margins, at one with the misfits, couch-hopping her way from one crisis to the next. It is the fiction she spins in order to keep her films honest.